In general, as a blow fan applied to a refrigerator, an inner rotor-type fan motor in which a rotor installed within a stator is rotated has been known, and in such an inner-rotor type fan motor, cooling air is circulatively supplied into a refrigerator according to its blowing operation.
Recently, an outer rotor type fan-motor that can be made compact with respect to a diameter direction and an axial direction is employed in consideration of an installation space within the refrigerator.
FIG. 1 is a perspective view of the related art outer rotor type fan-motor. As shown in FIG. 1, the outer rotor type fan-motor 10 includes a rear bearing assembly 14 substantially attached to a casing (not shown), a stator 11 attached to the rear bearing assembly 14, a front bearing assembly 13 attached to the stator 11, a rotor 12 having a rotational shaft 15, which is supported to be freely rotated by the both bearing assemblies 13 and 14, at its central portion, and a fan unit 20 installed at an outer circumference of the rotor 12.
In detail, the rotor 12 is disposed at an outer circumference of the stator 11 and has a cylindrical cup shape, and includes a permanent magnet 12a attached on an inner circumferential surface of the rotor 12. One end portion of the rotational shaft 15 is fixedly press-fit at a central portion of one end portion of the rotor 12.
With such a structure, in the so-called outer rotor type fan-motor 10, the rotational shaft 15 is rotatably supported by the front bearing assembly 13 and the rear bearing assembly 14, and the permanent magnet 12 is disposed to face the stator 11 with a slight space therebetween.
The fan unit 20 is made of a synthetic resin material and includes a hub 22 that covers the outer circumferential portion of the rotor 12 and a plurality of blades 21 extending in a diameter direction on an outer circumferential surface of the hub 22. An shaft fixing part 22a to be combined with the rotational shaft 15 is protrusively formed at the central portion of the hub 22.
The outer rotor type fan-motor 10 may be constructed by directly attaching the permanent magnet 12 on an inner surface of the hub 22.
With reference to FIG. 2, the outer circumference of the rotor 12 directly contacts and is combined with an inner surface of the bottom of the hub 22 of the fan unit 20.
The rotor 12 is rotated according to interaction between the stator 11 and the rotor 12, and as the hub 22 combined by directly contacting with an outer surface of the rotor 12 is rotated together with the rotor 12, the fan unit 20 is rotated.
Accordingly, in the related art fan motor 10 as described above, when the fan motor 10 is rotated, electromagnetic exciting force generated through the space between the stator 11 and the permanent magnet 12a excites the permanent magnet 12a and the exciting force is emanated through the fan unit 20 which directly contacts and is combined with the permanent magnet 12.
Meanwhile, in order to prevent vibration or noise of the permanent magnet 12 from being transferred to the fan unit 20, in some cases, an embossing surface is formed to minimize a contact portion in combining the rotor 12 or the permanent magnet 12 and the hub 22, but in this case, a partial noise is still emanated through the fan unit 20.
As for the emanated noise, in the related art outer rotor type fan-motor, as shown in FIG. 3, a large amount of high frequency noise is generated in the frequency range of 2000 Hz or higher. In addition to the problem of the generation of the high frequency noise, the high frequency noise has a bad influence on the durability of the outer rotor type fan-motor especially in a resonated state.